client/noop.go

@@ -588,7 +588,6 @@ func (n *noopClient) publish(ctx context.Context, ps []Message, opts ...PublishO
 
 	for _, p := range ps {
 		md := metadata.Copy(omd)
-		md[metadata.HeaderContentType] = p.ContentType()
 		topic := p.Topic()
 		if len(exchange) > 0 {
 			topic = exchange
@@ -600,6 +599,8 @@ func (n *noopClient) publish(ctx context.Context, ps []Message, opts ...PublishO
 			md.Set(k, v)
 		}
 
+		md[metadata.HeaderContentType] = p.ContentType()
+
 		var body []byte
 
 		// passed in raw data